Near infrared excitation/emission

Raman spectroscopy has been widely used to study the composition and molecular structure of polymers [100, 101, 102, 103, 104]. Assessment of conformation, tacticity, orientation, chain bonds and crystallinity bands are quite well established. However, some difficulties have been found when analysing Raman data since the band intensities depend upon several factors, such as laser power and sample and instrument alignment, which are not dependent on the sample chemical properties. Raman spectra may show a non-linear base line to fluorescence (or incandescence in near infrared excited Raman spectra). Fluorescence is a strong light emission, which interferes with or totally swaps the weak Raman signal. It is therefore necessary to remove the effects of these variables. Several methods and mathematical artefacts have been used in order to remove the effects of fluorescence on the spectra [105, 106, 107]. 

In this way green emission is obtained from near-infrared excitation. 

Figure 14 Improvement in the Raman spectrum of peat humic acid in neutralized form by use of near-infrared excitation. The top spectrum was obtained with 514.5-nm excitation, which results in a large fluorescence background that obscures the signal. However, as shown in the bottom spectrum, with 1064-nm excitation, and after subtraction of thermal emission background, spectral features of peat humic are clearly discernible. (Reprinted with permission from YH Yang, HA Chase. Applications of Raman and surface enhanced Raman scattering techniques to humic substances. Spectr Lett 31 821-848, 1998. Copyright 1998 Marcel Dekker, Inc.)...

Luminescence can be defined as the emission of light (intended in the broader sense of ultraviolet, visible, or near infrared radiation) by electronic excited states of atoms or molecules. Luminescence is an important phenomenon from a basic viewpoint (e.g., for monitoring excited state behavior) [1] as well as for applications (lasers, displays, sensors, etc.) [2,3]. 

Chemiluminescence (CL) is the emission of the electromagnetic (ultraviolet, visible, or near infrared) radiation by molecules or atoms resulting from a transition from an electronically excited state to a lower state (usually the ground state) in which the excited state is produced in a chemical reaction. The CL phenomenon is relatively uncommon because, in most chemical reactions, excited molecules... 

Dramatic advances in modem fluorophore technology have been achieved with the introduction of Alexa Fluor dyes by Molecular Probes (Alexa Fluor is a registered trademark of Molecular Probes). Alexa Fluor dyes are available in a broad range of fluorescence excitation and emission wavelength maxima, ranging from the ultraviolet and deep blue to the near-infrared regions. Because of the large... 

Two-photon emission is a process in which electronic transition between quantum levels occurs through the simultaneous emission of two photons. [27] presents more details about two-photon emission. Since metal clusters emit in the near-infrared region, they can be made useful for two-photon imaging with infrared excitation. Two-photon emission of Au25 clusters is observed at 830 nm by exciting at... 

Fig, 3. Transient absorption spectra of peridinin in methanol recorded in the visible (a) and the near-infrared (b) spectral regions after excitation at 490 nm in methanol (full squares) and at 535 nm in ethylene glycol (open squares). The transient absorption spectra in the visible region are normalized to the ESA maximum, while the near-infrared spectra are normalized to a maximum of the ICT emission. 

The discussion in Section II-B indicates that optical emission from 02(1E 7+) or 02(1A9) to the ground state may provide a useful method for the identification and estimation of the excited species. In laboratory studies, the (0, 0) bands, lying at about 7620 A and 1.27 [x, respectively, are likely to be the strongest. The emission at 7620 A is relatively easily detected by suitable photomultipliers, and spectra may even be recorded with photographic emulsions sensitive to the near infrared (such as the Kodak N coating). Trialkali (S20) photocathodes combine a high sensitivity with low dark current, and photomultipliers with an S20 cathode... 

The principal reaction discussed above forms oxygen molecules in high vibrational levels of the ground state. This is chemi-excitation but is not chemiluminescence vibration-rotation transitions of homonuclear molecules are forbidden. For such cases electronic absorption spectroscopy is the required technique. For reactions in which a heteronuclear diatomic (or a polyatomic) molecule is excited these transitions are allowed. They are overtones of the molecular transitions that occur in the near infrared. These excited products emit spontaneously. The reactions are chemiluminescent, their emission spectra may be obtained and analyzed in order to deduce the detailed course of the reaction. 

The lower energy luminescence of Os(II) complexes relative to the corresponding Ru(II) complexes has led to a number of studies seeking complexes that absorb throughout the visible (black chromophores) and have emissive excited states in the near-infrared. Kol and Barigelletti reported the photophysical properties of Os(II) complexes of eilatin (eil, Scheme 1) and isoeilatin (ieil) bis-phenanthroline derivatives. The eil com-... 

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